A common problem that occurs in radio transmission of signals is that the signals are lost as a result of interference and fading. This problem is evident in mobile radio transmissions in which a mobile receiver moves in an interference field with frequently recurring fading. The receiver receives radio signals over a channel which is liable to disturbance. The signals are received on the antennas, which are mutually spaced apart, and sampled. A channel estimate is formed, and signal processing in an equalizer of the Viterbi-receiver in accordance with the Viterbi-algorithm. One known method of reducing the influence of fading is to use a receiver which has two or more mutually spaced antennas, for instance as described in Electronics Letters, Jul. 20, 1989, Vol. 25, No. 15, L. B. Lopes: Combined Space/Time Diversity Technique for Narrowband TDMA Mobile Radio Systems. A transmitted digital radio signal is received by a first antenna and is delayed in time by a suitable selected time interval. The radio signal is also received by a second antenna whose signal is added to the delayed signal and the summation signal is processed in an equalizer, which may be a Viterbi-equalizer. The article discloses that the bit error content decreases in accordance with the length of the delay interval. An alternative method is one of using receivers that are equipped with several antennas, as described in Mobile Communications Design Fundamentals by William C. Y. Lee, Howard W. Sams & Co, Indiana, USA. In section 3.5.1 of this book several examples are given as to how signals from two receiver amplifiers with separate antennas can be added in order to counteract fading. In the case of digital signal transmission this addition results in the difficulty of necessitating phase correct addition of the signals. The signals received by the individual antennas may be in counter-phase and extinguish one another, even when the signals received by the antennas have a satisfactorily high strength. Consequently, it is necessary to phase-lock the signals, which is difficult to achieve, particularly with a rapidly fading channel which is subjected to noise disturbances. Slow, variable phase-locking is used advantageously in the case of such noise disturbances, whereas the rapid fading requires rapid, variable phase locking.